The present invention relates to a cooling system and more specifically relates to an evaporative cooling system on the exterior of a structure to radiate away solar heat.
All of the references mentioned below are incorporated by reference herein.
Numerous systems and considerable energy resources have been used to regulate the temperature within buildings and other structures. The cost of electricity for such systems is quite considerable. In many homes, an area below the roof joists and the interior ceiling acts to contain air heated by the solar radiation impinging upon a roof. The air contained within this space is vented from side vents of the interior space. Additional insulation on the ceiling acts to reduce heat transfer from this space. However, a number of structures do not have such spaces between the ceiling and the roof of the structure or such spaces are minimal. Such structures include mobile and manufactured homes. Many of these types of buildings have vaulted ceilings with minimal space between the interior ceiling and the roof.
A number of air conditioning devices have been developed to cool interior of structures. Such devices are generally heat pumps that introduce cool air into a room. Given the cost of operating such air conditions, an alternative of supplementary means for cooling structures is desirable.
In addition to insulating a ceiling space, cooling a roof has been proposed as a means to reduce temperature within a structure.
U.S. Pat. No. 1,808,829 to Barnes discloses the use of a fabric such as burlap or canvas for evaporative cooling of a building. The fabric is positioned on a building""s roof and is wetted. The water is allowed to evaporate, cooling the structure. This method has certain drawbacks however. The material used could be damaged by wind or degraded by rotting or rodent infestation. In addition, no automated application of the water is provided. Such a system would require constant monitoring to ensure the fabric remained wet.
U.S. Pat. No. 2,266,321 to Holder discloses a network of pipes through which water may be directed onto a roof surface. An automatic valve linked to a heat sensor regulates flow of water. The heat sensor is enclosed in a vented enclosure mounted on the roof. A thermal expansion within the bulb creates a pressure that actuates the valve controlling the dispensing of water throughout the pipes. The pipes extend over the surface of the roof and have spray heads to distribute the water.
U.S. Pat. No. 2,660,863 to Gerhart discloses a system for evaporative cooling of a structure surface using a porous hose, such as a canvas tube, to apply water over a time interval to a roof surface. The tube is positioned near the apex of the roof allowing water to drip down over the surface of the roof. Water that travels over the roof to the edge of the roof without evaporating is collected from the gutters at the edge of the roof. This water returns to a storage location for reapplication to the roof surface. The canvas hose may be subject to environmental decay.
U.S. Pat. No. 4,761,965 to Viner discloses a network of roof water pipes having periodic nozzles for applying a spray of water in a uniform manner over the surface of a roof. The sprayed water evaporates to cool the roof. An electronic temperature sensor measures the roof temperature. When the roof temperature rises above a temperature set point, the spray system is activated. The system includes a pressure regulator to ensure proper water pressure level at the nozzles. This controls and regulates the spray pattern. The control system also applies the water by activating the valves at cycled periodic intervals. This ensures more even temperature regulation of the roof surface.
U.S. Pat. No. 6,250,091 to Jerome discloses another similar system for cooling a building. In this system, a network of delivery water pipes extends across a roof surface. A number of spray nozzles are periodically disposed along the pipe length. A number of sensors measure the temperature of the roof. In addition, sensors measure the moisture remaining on the roof. The sensors are joined to electrically operated valves that apply the water at desired intervals. The nozzles are operated in sequence to reduce the water pressure required for operation of the spray nozzles. The array of nozzles are segregated into a number of defined areas. In each area a valve controls water flow. The valve is actuated in response to signals from separate moisture and temperature sensors. In this manner, if one area of a building receives an increased amount of solar energy, the system will compensate by spraying additional water on that area.
U.S. Pat. No. 6,367,275 to Stephan discloses a method of evaporative cooling using a mixture of cement and aluminum powder. The concrete is placed on the roof and water is applied to allow for evaporative cooling. The concrete is applied in a 3 to 6 cm thickness and adds considerable weight to the roof. In addition, the concrete pour may only be done on flat roofs.
A number of the prior evaporative cooling systems share certain drawbacks. None of the prior art systems effectively act as a barrier to solar radiation impinging on the exterior surface of a building, such as a roof or exterior wall area. Such devices cannot have an insulating effect. In addition, these systems will not reflect solar energy. Because the total solar energy is still hitting the roof, additional water or other cooling will be required to dispel this absorbed energy.
The use of a thermostat on a roof on which the sun impinges is also problematic. The thermostat or other temperature-sensing device will be heated by the air and will be difficult to thermally isolate. In addition, it will in many cases be difficult to attach the thermostat to a roof surface such that efficient heat transfer from the roof allows measurement of roof temperature. For example, the surface of wood shingle roofs is highly variable. On such a roof it would be difficult to form an epoxy bond with this porous and variable surface. Temperatures measured by the thermostat on any surface may not accurately measure roof temperature and may instead measure the ambient air temperature, which may be considerably warmer or cooler than the roof.
Systems having moisture sensors also have potential drawbacks. Such a system would attempt to regulate temperature using moisture measurement, an indirect measurement method. On a dry, cloudy, windy day during conditions of low humidity, a moisture sensor for detecting moisture of the roof could activate the system even if the roof were cool.
Systems having large numbers of sensors and electronics are expensive and multiply the risk of some element of the system breaking down.
Spray application of water is also potentially problematic. Greater water pressure is required to spray the water with sufficient force to atomize the water into droplets and propel the droplets over a roof area. Such distribution of water over the roof is bound to be uneven due to gravitational forces. Because roof pitch will vary from structure to structure, spray applicators will also have to be altered to accommodate steeper roofs. The use of spray systems on sheer walls is unlikely to evenly apply water. In addition, some water of the spray will be evaporated prior to contacting the building exterior. The effects of such evaporation in cooling the roof will be minimal. Also, wind can blow the spray, changing the application pattern on the roof and requiring additional application of water. Such spray nozzles can clog, requiring maintenance.
The present invention is a system for cooling a structure. The system includes a polymeric sheet for covering an area of the exterior of the structure, such as a wall or roof section. Integral with the polymeric sheet is a water distribution system that allows wetting of the sheet. The water distribution system (such as a series of drip lines) is joined to a water supply tube linked to the water supply for the structure. A valve regulates water flow through the supply tube to the distribution system. A sensor associated with the sheet senses an environmental parameter, such as moisture in the sheet or temperature between the sheet and the roof. The sensor electrically signals the control system that operates the valve. When the roof temperature reaches a selected temperature, the valve is actuated and water flows to the distribution system. Alternatively, when the sheet becomes dry, the valve may be activated.
A number of different embodiments and implementation of this system are possible. The polymeric sheet may include features that reflect solar energy. The upper side of the sheet upon which solar radiation impinges may be selected to reflect solar radiation. Any color that reflects more solar energy than the original building surface is suitable, including light colors and gray. White would be an efficient reflective surface, as would a metallic mirroring surface, such as would be obtainable by using Mylar(copyright). This would reflect considerable solar radiation.
The system would also include a means for attaching the sheet to the surface of the structure to prevent the sheet from blowing off. The sheet may be secured by a network of lateral and transverse cables that are attached at the apex and edges of the roof or wall. An alternative could be the use of a mesh material such as plastic netting affixed to the bottom of the polymeric sheet of material. This mesh could be attached to the edges of a roof or wall of the structure.